Mechanisms of oxygenation responses to proning and recruitment in COVID-19 pneumonia

Abstract

Purpose: This study aimed at investigating the mechanisms underlying the oxygenation response to proning and recruitment maneuvers in coronavirus disease 2019 (COVID-19) pneumonia.Methods: Twenty-five patients with COVID-19 pneumonia, at variable times since admission (from 1 to 3 weeks), underwent computed tomography (CT) lung scans, gas-exchange and lung-mechanics measurement in supine and prone positions at 5 cmH 2 O and during recruiting maneuver (supine, 35 cmH 2 O). Within the non-aerated tissue, we differentiated the atelectatic and consolidated tissue (recruitable and non-recruitable at 35 cmH 2 O of airway pressure). Positive/negative response to proning/recruitment was defined as increase/decrease of PaO 2 /FiO 2 . Apparent perfusion ratio was computed as venous admixture/non aerated tissue fraction. Results:The average values of venous admixture and PaO 2 /FiO 2 ratio were similar in supine-5 and prone-5. However, the PaO 2 /FiO 2 changes (increasing in 65% of the patients and decreasing in 35%, from supine to prone) correlated with the balance between resolution of dorsal atelectasis and formation of ventral atelectasis (p = 0.002). Dorsal consolidated tissue determined this balance, being inversely related with dorsal recruitment (p = 0.012). From supine-5 to supine-35, the apparent perfusion ratio increased from 1.38 ± 0.71 to 2.15 ± 1.15 (p = 0.004) while PaO 2 /FiO 2 ratio increased in 52% and decreased in 48% of patients. Non-responders had consolidated tissue fraction of 0.27 ± 0.1 vs. 0.18 ± 0.1 in the responding cohort (p = 0.04). Consolidated tissue, PaCO 2 and respiratory system elastance were higher in patients assessed late (all p < 0.05), suggesting, all together, "fibrotic-like" changes of the lung over time. Conclusion:The amount of consolidated tissue was higher in patients assessed during the third week and determined the oxygenation responses following pronation and recruitment maneuvers.

Prone Position and COVID-19: Mechanisms and Effects*

“…In summary, the improvement (or the lack of improvement) in oxygenation in COVID-19 patients depends on the interplay among the mechanisms described. At this stage of the disease (within 1 wk from intubation), the recruitment is one of the possibilities, but likely, not the most important, as strongly suggested by the lack of correlation between recruitment and oxygenation, a finding similar to what recently found with the CT scan in COVID-19 patients when studied at the same stage of the disease ( 14 , 15 ).…”

“…Finally, in late stages of the disease, the likelihood for oxygenation to improve with prone positioning becomes extremely low. We recently found that this phenomenon may be due to the progression of lung consolidation toward organizing fibrotic pneumonia ( 14 ).…”

Orthodeoxia and its implications on awake-proning in COVID-19 pneumonia

“…In conclusion, orthodeoxia appears a common clinical feature of early COVID-19 pneumonia. This novel finding contributes to further distinguishing COVID-19 from other causes of ARDS [ 1 , 2 , 6 ], while reinforcing its advocated similarity with HPS [ 3 , 4 ]. Additionally, detecting orthodeoxia may help avoid awake-pronation when oxygenation simply benefits from recumbency: in a pandemic scenario, this possibly relevant clinical implication would deserve confirmation by larger studies.…”

“…During proning, patients with and without orthodeoxia behaved similarly: respectively, 6 (46%) and 5 (36%) were prone responders ( p = 0.70, median PaO 2 increase 65[30–92] mmHg). This suggests that orthodeoxia cannot anticipate the response to proning, likely because of the unpredictable balance between perfusion redistribution and parenchymal reaeration in the ventral position [ 6 ]. However, the finding of orthodeoxia avoided overestimating the benefits of awake-pronation in 6 patients (22%) whose oxygenation improvement was due to lying recumbent at 0°, irrespective of prone or supine specifically (Fig.…”

Effect of proning and recruitment on physio-anatomical variables in COVID-19 pneumonia

“…We read with interest the study done by Rossi et al recently published in Intensive Care Medicine [ 1 ]. In this study, the authors have studied the anatomical and physiological bases of oxygenation response to proning and recruitment maneuvers (RM) in acute respiratory distress syndrome (ARDS), by assessing gas exchange, lung mechanics, computed tomography (CT) chest scans and hemodynamics in coronavirus 2019 disease (COVID-19) patients with varied time period (3–24 days after hospital admission) [ 1 ]. Their findings are suggestive of lesser benefit of recruitment on oxygenation by the third week of illness in COVID ARDS.…”